Protective relay system



Nov. 8, 1932. s. SUNAIRI PROTECTIVE RELAY SYSTEM Filed Aug. 22, 1928Referring now to the drawing, wherein Figure' 1 shows a diagram ofcircuits and apparatus embodying my invention, a substation 1 receivesalternating current electrical power from a power station 2, by way of adouble-circuit high tension transmission line, comprising two circuits 3and 4, including circuit interrupters 5 and 6 at the receiving end, andcircuit interruoters 7 and 8 at the sending end, r spectively. point ofthe system 2 is not grounded, or alternately, it may be grounded througha high limiting resistance as hercinbcfore described. But it will not benecessary to illustrate this grounding resistance, because such anarrangement may be readily understood.

l/Vith the sending ends oia the respective circuits are associatedcurrent transformers 9V and 10, whose secondaries are differentially oroppositely connected for respective corresponding phases, with theirstar points grounded, and energize a directional power relay 11.

The relay 11 comprises current windings 12 connected between respectivephases of the current transformers and the ground, and potentialwindings 13 energized in accordance with the phase voltages at the powerstation. The potential windings may be conveniently energized from thelow tension side oi lthe main transformers 14, through a potentialtransformer 15, it necessary. With this arrangement, considerableexpenses in providing a high tension potential transformer may beavoided.

The directional power relay also comprises two opposed pairs of contacts16 and 17 ycontrolled by an armature 18 carrying a movable Contact, forselectively engaging the contacts 16 and 17 in accordance with theenergization of the actuating windings 12 and 13. The contacts 16 and 17control the tripping circuits of the circuit interrupters 7 and 8.

It must be noted that this relay 11 is so arranged that the armature 18is actuated to one direction, say tothe lett when a shortcircuit currentflows in one circuit, say 3, which current always lags from the normalvoltage of the power system, while it is actuated to the oppositedirection, i. e., to the right when a ground current flows in the samecircuit 3, as hereinbeiore described.

In circuit with each current winding 12, there is` included the windingof an overload relay 19, 29 or 21, and these windings are stanconnectedat the outer terminals .of the overload relays. Between the star pointand the earth is included the windings of two ground current relays 22and 23, in series. It will be readily understood that these groundcurrent relays will not be energized unless a ground current flowstherethrough due to the grounding ol one circuit, because he shortcircuit current or load current bal- 'llhe neutral n ances with eachother within the star-connected windings of the relays 11 and 19, 20 and21.

The contacts of the overload relays 19, 2O and 21, and of the groundcurrent relay 22 are connected inparallel relation with each other, andconnected between the multiple contacts 16 and 17 of the directionalpower relay 11 and the negative side of a direct current control line,while the contact of the other ground relay 23 is included in theenergizing circuit for a change-over relay 24 across the control line.The relay 24 is provided with four pairs of contacts 25, 26, 27 and 28,and a movable armature 29, arranged so as to change over the circuitsconnecting the contacts 16 and 17 and the tripping coils 7 and 8 ot thecircuit interrupters 7 and 8, in a manner as hereinafter described.

ln order to rovide a better understandin@ oi the invention, I will nowdescribe the operation of selective protection which takes place in caseof one faulty circuit.

Now assume that a short-circuit has occurred in the circuit 3, while theother circuit el is normal. Unbalanced current will then flow throughthe current windings 12 and those of the overload relays 19, 20, 21, butthese currents balance with each other within these star-connectedwindings; no-

current will flow to the ground curr-entrelays 22 and 23. The contactsof the overload relays are thus closed and the armature 18 is actuatedby the lagging short-cir cuit current to eno'ae the contacts 16. The

tripping circuit of the iiaulty circuit 3 is thus comnleted from oneside of the control l L line through the tripping coil 7, contacts 25,16, and contacts 19, 20, 21 in multiple to the other side of the controlline, and the interruptor 7 is tripped to its open position.

W hen one line of the circuit 3 is grounded by fault while the othercircuit 1 is normal, a ground current will flow through the currentwindings 12 and the windings of the ground current relays 22 and 23 tothe ground,

and energize them. The armature 18 is then actuated in the direction toengage the contacts 17, while the relayY 23 closes its contacts, andcompletes the energizing circuit of the change-over relay 211. Thearmature 29 is then yoperated to the upper position shown. rhe trippingcircuit of the circuit interrupter 7 is thus completed from one side Yof the control line through, the tripping coil 7 the contacts 27, 17 andthe contacts of the relay 22, which is now energized, to the otl nerside .of the control line. The interrupter 7 lil() circuit of the othertrippingcoil 8 would be undesirably completed.

By some reason, such as in the case that the grounding would haveoccurred at a point adjacent to the receiving end, it would happen thatthe circuit Iinterruptor 5 is first tripped before the properinterrupter 7 is open. In this case, the whole load is transferred tothe other circuit 4, increasing its load current, while in the groundedcircuit 3 there flows the leading ground current only. As is obviousfrom the abovementioned special arrangement and setting of the relay 11,both the lagging current in the circuit e' and the leading current inthe circuit 3, function to actuate the armature 18 in one and the samedirection so as to complete the tripping circuit of the properinterruptor 7.

When a grounding and a short-circuiting should have occuredsimultaneously, the differential currents in the relay windings 12 andthe respective windings 19, 20, 21 are the sum of the largeshort-circuit current 1and the relatively small ground current,

whilel through the ground current relays 22 and 23 there flows theground current only. The relay 11 then operates its armature 18 to theleft position, due to the fact that the vectorial sum of heavyshort-circuit current d relatively small ground current has such a phasethat the relay produces a torque in the same direction with the.short-circuit current only. The energizing circuit of the tripping coil7 is thus completed across the control line through coil 7 contacts 25and 16, and contacts of the relays 19, 20, and 21 in multiple, and thefaulty circuit 8 is interrupted at the interruptor 7. It will be readilyunderstood that the overload relay must have a time limit sooner thanthat of the ground current relay 23, for the large short-circuitcurrent.

In an ordinary watt-hour meter type rclay, the torque is maximum whenthe voltage current are in phase with each other, that is to say, thecurrent in voltage winding is made to lag the terminal voltage thereofby 90 degrees, that is to say, the power factor of voltage windingcircuit is made zero.

Consequently, the torque is maximum when the current in current windingis in phase with the terminal voltage of voltage winding, as the torqueis maximum when the current flux and voltage iux have 90 degrees phasedifference with each other. Therefore, the torque is zero when thecurrent in current winding and the terminal voltage of voltage windinghave 90 degrees phase difference.

In the present invention, the power factor of voltage winding circuit isnot made zero, but has a suitable substantial value, and by properselection of the power factor, the relay made to have its torque zerowhen 'I line current of the system leads line voltage by a certainangle. -With the connection of the relay 11 shown in the drawing, avector diagram for the relay is given in Figure 4, wherein P1 representsthe voltage impressed on the voltage winding of one phase, which is theline-to-line voltage of the system, while Il represents the current inthe current winding of the same phase, which is in phase with the linecurrent. According to the invention, assume thatthe power factor ofvoltage win ding circuit is made 0.5, that is to say, the currenttherein lags the terminal voltage by degrees. P11 then represents thecurrent in voltage winding. The torque will be zero when Il and P11 arein phase or in opposite phase with each other. This condition occurswhen Il is shifted forward by 80 degrees and takes the position of Il',and this signifies that the line current Il leads the phase voltage Elby 30 degrees.

The directional relay has normally a zero torque relationship as taughtby the position of the vectors Il and PI in Figure t and such zerotorque relationship ceases to eXist when a. short circuit or groundoccurs on the system to be protected because of the change of theposition of these two vectors.

Although I have shown only one embodiment of my invention, it will bereadily understood that various modifications and changes are possible,and l do not intend to limit myself by the specific disclosure out onlyinsofar as xSet forth in the appended claims.

I claim as my invention:

1. A protective system adapted for use in a grounded neutral systemincluding a high resistance to ground or a non-grounded system, adouble-circuit transmission system of such a nature that the faultyground current is often lower than the load current in the circuit,means for interrupting said two circuits at the power station end,respectively, a directional power relay for controlling saidinterrupting means and comprising current elements energized inaccordance with the unbalance between said two circuits and potentialelements energized in accordance with the normal phase voltages of thepower station, and a change-over relay operated in accordance with aground current for reversing the connection of said interrupting meanswith the contacts of said directional power relay.

2. A protective system adapted for use in a grounded neutral systemincluding a high resistance to ground or a non-grounded system, adouble-circuit transmission system of such a nature that the faultyground current is often lower than the load current in the circuit,means for interrupting said two circuits at the power station endrespectively, a directional power relay for selectively controlling saidinterrupting means in accordance with leading current and laggingcurrent which flows in'one circuit when it is cuits respectively at thepower station end,

`int-2ans 'for selectively controlling said interrupting means inaccordance with. lagging current which flows in one circuit when it isshort-circuited and means for reversing the function of said first meansin accordance with a .grounding of said circuit.

4. A protective system adapted for use in a grounded neutral systemincluding a high resistance to ground or a non-grounded system, adouble-circuit transmission system of such a nature that the faultyground current is often lower than the load current in the circuit, adirectional power relay comprising an opposed pair of contacts, aplurality of current windings energized in accordance with the unbalancebetween respective corresponding phases of said two circuits, aplurality of potential windings energized in accordance with therespective phase voltages in the power station end, and acontact-carrying movable armature actuated thereby, said relay being soarranged that the actuating torque is zero when the current leads thephase voltage in phase by a predetermined degree, a change-over relayfor reversing the connection of said pairs of contacts, and a groundcurrent relay for energizing said change-over relay.

5. A protective system adapted for use in a grounded neutral systemincluding a high resistance to ground or non-grounded system, apower-station, a transmission line of such a nature that the faultyground current is often lower than the load current -in line.I a circuitinterrupter having a tripping coil for cutting out said line from saidpower station, a directional power relay for controlling the circuit ofsaid tripping coil of said interrupter, said relay comprising acontactcarrying movable armature which is actuated in one direction inaccordance with the ground current when said line is grounded, so as toprepare one tripping circuit, and is actuated in the opposite directionin response to short-circuit current in said line, so as to prepareanother tripping circuit, a current relay energized by said groundcurrent for completing a control circuit, and a second cur- In witnesswhereof I affix my signature. f SHIZ SUNAIRI.

